1. Field of the Invention
The present invention relates to a linear guide apparatus and a method for assembling the linear guide apparatus.
2. Description of the Related Art
A example of a related-art linear guide apparatus is shown in FIG. 9. As shown in this drawing, the linear guide apparatus includes a guide rail 1, a slider (also called a bearing) 2, and a plurality of balls (rolling elements) 3.
The guide rail 1 has a pair of ball rolling grooves 11 respectively provided in both side surfaces thereof and extending parallel to the longitudinal direction. The slider 2 includes a pair of leg portions 2A respectively disposed on widthwise both sides of the guide rail 1, and a horizontal portion 2B connecting both leg portions 2A. The horizontal portion 2B is disposed at one end side (in this drawing, on the upper surface side of the guide rail 1), as viewed in the thicknesswise direction (i.e., in a direction perpendicular to both the longitudinal direction and the widthwise direction), of the guide rail 1. Both inner side surfaces of the slider 2 are disposed in face-to-face relation to both side surfaces of the guide rail 1.
The slider 2 is divided into a main body 21 and a pair of end caps 22 in the linearly moving direction, and the end caps 22 are respectively disposed on both ends, as viewed in the linearly moving direction, of the main body 21. A pair of ball rolling grooves 21a respectively opposing the ball rolling grooves 11 of the guide rail 1 are formed in each of both inner side surfaces of this main body 21. A ball rolling path 12 of the balls 3 is formed by the ball rolling grooves 11 and 21a. 
A linear return path 21b is formed on the outer side of each ball rolling groove 21a of the main body 21 of the slider 2. A pair of semicircular arc shaped direction changing paths 22a are each formed in that portion of the respective end cap 22 (a longitudinally outer portion of each end cap 22) which is disposed on each side surface of the guide rail 1. The ball rolling path 12 and the return path 21b are made to communicate with each other by these direction changing paths 22a. Three paths constitute a circulating path 25 for endlessly circulating the balls 3. This linear guide apparatus has four (two pairs of) circulating paths, and as the balls 3 roll along the circulating paths, the slider 2 slides along the guide rail 1.
In the related-art linear guide apparatus, the return paths 21b are formed in the metallic main body 21 by drilling, but this operation requires time and trouble and involves cost.
As an alternative method, a method is disclosed in JP-UM-A-61-85716 and the like in which a groove with a concave cross section is provided in an outer side surface of each leg portion of the slider. This groove is covered by a closing member, and both longitudinal ends of this closing member are respectively fixed to end caps. In this method, the return path is formed by both the groove and the inner surface of the closing member.
With the method of the above-described publication, however, the number of component parts becomes greater than that of the method in which the metallic main body is subjected to drilling, so that assembly becomes complex. In a case where the fixation of the closing member becomes insufficient, the component parts vibrate and generate noise.
In addition, JP-B-2846050 discloses a technique in which the slider is divided into a metallic block, a substantially square annular body made of a synthetic resin, and a pair of synthetic resin-made plates. As viewed in the widthwise direction, each of both leg portions of this slider is divided into the block, the substantially square annular body, and the plate. Further, as viewed in the thicknesswise direction, each leg portion (a widthwise outer portion of the leg portion) is divided into two parts of the substantially square annular body and the plate. Further, a groove of a shape in which a return path and a pair of direction changing paths formed continuously are divided into two parts as viewed in the thicknesswise direction is formed in each of the substantially square annular body and the plate.
In the slider disclosed in this publication, since the direction changing path is formed by the groove divided into two parts as viewed in the thicknesswise direction, a scooping portion called a tongue for causing the rolling elements to move from the ball rolling groove to the direction changing path (or vice versa) is also made up by two divided bodies as viewed in the thicknesswise direction. Therefore, as compared with the case where the tongue is made up by a nondivided body, the strength of the tongue declines.
As a proposal which makes it possible to overcome these problems, JP-A-7-317762 discloses a technique in which at least the widthwise outer portion of the leg portion (the portion where the return path is formed) is formed integrally with a block as a molded piece made of a synthetic resin, thereby forming the slider in which the return path is formed by a nondivided body.
However, in the case of the slider disclosed in JP-A-7-317762, a molded piece having the widthwise outer portions of the leg portions is fixed to the block by integral molding, so that correction after molding is difficult. In addition, since the structure of a mold for integral molding becomes complex, there is leeway for improvement in terms of productivity.
Namely, in the slider disclosed in JP-A-7-317762, since the slider is continuously covered with the resin, it is utterly impossible to effect correction including the correction of such as the depth or the shape of the ball rolling grooves after molding. Accordingly, in a case where adjustment of a preload and improvement of the actuation characteristic are required, the resin must be destroyed. In addition, since the resin is allowed to flow with a small thickness around the periphery of the slider, particularly since the resin is allowed to flow in an elongated form along the longitudinal direction of the slider, molderability is poor, and the structure of the mold is complex. Further, since the steps of placing the slider in the mold and cooling it after molding are required, processing takes time.